ANATOMY OF THE EYEBALL. 



57 



FIG. 2. 



A. 



is difficult to make out any thing but an entirely homogene- 

 ous structure ; but shortly after death each rod seems to be 

 divided by a delicate line into an outer and an inner seg- 

 ment, the outer being a little the longer. At the upper ex- 

 tremity of the inner segment, is a 

 hemispherical body, with its con- 

 vexity presenting inward, called 

 the lentiform body (linsenformi- 

 ger Korper}. The entire inner 

 segment is somewhat granular, 

 and often presents a granular nu- 

 cleus at its inner extremity. The 

 outer segment apparently differs 

 in its constitution from the inner 

 segment, and is not similarly af- 

 fected by reagents. Treated with 

 dilute acetic acid, the outer seg- 



' O 



ment becomes broken up trans- 

 versely into thin disks. These 

 points in the anatomy of the rods 

 are referred to particularly, for 

 the reason that they have lately 

 been used as an anatomical basis 

 for a theory of the perception of 

 colors. 1 They can be readily un- 

 derstood by reference to Fig. 2. 



The cones are probably of the same constitution as the 

 rods, but that portion called the inner segment is pyriform. 

 The straight portion above (the outer segment) is sometimes 

 called the cone-rod. The entire cones are about half the 



retina is to be found in the Journal de Tanatomie, Paris, 1869, tome vi.. pp. 438, 

 543, 648. As regards the structure of the rods and cones, the views of Schultze 

 are now pretty generally accepted by anatomists. (SCHULTZE, Ueber Stdbchen und 

 Zapfen dcr Retina. ArcUv fur mikroskopische Anatomic, Bonn, 1867, Bd. Hi., 

 S. 215, et seq.) 



1 ZEXKER, Versuch einer Theorie der Farben-Perception. Archiv fur mikro- 

 scopische Anatomic, Bonn, 1867, Bd. hi, S. 248, et seq. 



From the monkey. A. Eods, after ma- 

 ceration in iodized serum, the outer 

 segment (6) truncated, the inner seg- 

 ment (a) coagulated, granular, and 

 somewhat swollen; c, filament of 

 the rods ; rf, nucleus. B. Eods from 

 the frog. 1. Fresh, magnified 500 

 diameters, a, inner segment ; &, 

 outer segment; c, lentiform body; 

 d, nucleus. 2. Treated with dilute 

 acetic acid and broken up into plates, 

 magnified 1,000 diameters. Taken 

 from Schultze's figures. (KOLLi- 

 KEB, Handbuch der G&webelehre, 

 Leipzig, 1867, S. 6TO.) 



